Groundwork & Foundations Question

Suitable hardcore for extension?

We are in the process (2wks in)of building an extension (3x9m). The oversite is due to start next week.

- The architect has specified 150mm hardcore but it seems the builder was not planning to lay this as the ground had not been dug out at all and he was planning to just lay the sand and the DPM etc - is this normal?
We have subsequently raised this issue with the builder and they are now proceeding to dig out the ground, although they are claiming MOT hardcore is already present from a previous patio. we are unsure if this is suitable for an extension. To us, the ground just looks like topsoil - we can see roots growing in it when we dig down into it!

- The architect also specified 80mm Celotex for the floor insulation - the builder decided to change this to Jablite which I believe is cheaper and inferior? He didn't tell us he had changed it. Since we now require a thicker layer of this insulation, he needs to make compromises with the other layers in the oversite (hence not doing the hardcore)

- The bricklayer put dishwashing liquid in the mortar - have just seen on the MyBuilder forums that this is unacceptable practice. How concerned should we be about this?

Any advice much appreciated.

5 Answers

Best Answer


My suggestion would be to stop work and find another builder while you are at this stage. Nothing so far is irrepairable but if you allow him to continue it may cost you a lot of money!!

150mm mot is a must in the sub base of an extension, thats why it is in the spec!! Jablite is very poor insulation and again, not specified in the drawings! As for fairy in the mortar........thats just poor practise and not to be expected of a proper bricklayer!! As another has said dont let them lay in this weather, it should be 3 degrees plus as a minimum and frostproofer is a waste of time, so dont let them fob you off with that either.

You seriously need to take action now or you will face bigger problems. It may mean waiting a month for someone else to be free (in my case 7 months) but it is a much better option than continuing with these guys!!!

Answered 4th Apr 2013

R.Hughes Building and Conservation Ltd

Member since 25 Feb 2009

Firstly, if there are drawings for the builder to follow and he was given them when he priced. Are these details in the drawings? And if so then they should be followed. Don't be affraid to stop works till you get what you want. Your paying them to do a job. There's nothing wrong with recycling but only if its clean. Sounds like he's priced the job to cheap and trying to make up for it.

As much as architects love to spect the dear stuff, don't skimp on the insulation. It will give the required U value you need to meet building regs. Celotex is foil backed and jablite is just polystyrene. Probably half price.

I wouldn't be to concerned about the fairy. There will be some tech guru to prove me wrong and I do use sika concentrate now . I would be more concerned if he's using frost proofer in this weather and covering the work at night as the moisture in cement expands and it looses its cohesion.

Answered 2nd Apr 2013

Contour Landscapes

Member since 26 Sep 2010

Why not ask your building control officer to sort the builder - that is what you paid them for, he is there to ensure the job is done properly and is on your side - the builder will be unlikely to argue with him. As for the squeezy in the mortar - It used to be used to create elasticity in the mortar to make it easier to work with. It is now known that a lot of washing up liquids contain soluble salts which can lead to efflorescence, they can also be hygroscopic and attract moisture from the air into the mortar. mortar plasticiser is actually cheaper than squeezy, comes in 5L containers (or in powder form) for about a fiver depending where you buy. Of course if the builder uses your squeezy he saves his fiver.
Mike Davison cssw
Dryspace Maintain specialist construction services.

Answered 2nd Apr 2013

Dryspace Maintain Ltd

Member since 7 Nov 2010

ALARM BELLS should be ringing all tell tale signs of Cowboy builders!

Answered 1st Apr 2013

Electrical Safety Services

Member since 17 Oct 2011

Sounds like you have a bit of a corner cutter or an incompetent.Jablite is much cheaper and is very inferior.At this stage he doesn't seem to be thinking much about building regs or getting things done properly.I wouldn't be employing someone that ignores an approved plan to make it up as they go along:)

Answered 1st Apr 2013

Roc builders

Member since 25 Aug 2011

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